Added a top-bar button that links to the GitHub repo

[mikesamuel]

Addresses #15

[mikesamuel]

The GitHub logo comes from https://github.com/logos which explicitly allows its use for linking to GitHub.

[MylesBorins]

Mostly looks good. Since the github logo is a direct link it is now resizing on hover, which is inconsistent with the other buttons

[mikesamuel]

I'm guessing that's related to some :hover default gitbook styles.

[MylesBorins]

Following diff fixes it

diff --git a/styles/website.css b/styles/website.css
index a9f02de..81c790a 100644
--- a/styles/website.css
+++ b/styles/website.css
@@ -26,12 +26,13 @@

 .github-button.btn.links-link {
     display: inline-block;
-    width: 32px;
+    width: 30px;
     font-size: 0;
     background-image: url("/images/GitHub-Mark-32px.png");
     background-repeat: no-repeat;
     background-position: center center;
     opacity: 0.25;
+    background-size: 20px;
 }

although it doesn't have a highlight on hover, but we can fix that in a followup as the other custom link doesn't have it either

[mikesamuel]

Folded your fix into this PR. Thanks.